A conventional electrodeless discharge lamp has no electrode formed inside a light emitting tube, so that in contrast to a general discharge lamp such as a fluorescent lamp, it is free from a lighting failure due to electrode break. Thus, it has the advantage of longer life than a general fluorescent lamp or the like.
As shown in Published Japanese Translation of PCT Application Hei 11-508404, for example, an example of such a known electrodeless discharge lamp fills a discharge gas in a bulb, and applies a high frequency electromagnetic field thereto so as to excite the discharge gas in the bulb for emitting light.
This electrodeless discharge lamp comprises a lamp part as a light emitting body and a coupler member fitted to the lamp part. The lamp part has a bulb containing a discharge gas, and a base which fixes and supports the bulb and which is fitted to the coupler member. The coupler member, which forms an induction coil, has a coil and a heat conductive body for generating electromagnetic energy as well as an attachment member to be fitted to the base. The base and the attachment member of the coupler member are respectively formed of synthetic resin, enabling the lamp part to be attached to and detached from the coupler member, and preventing the lamp part from being easily detached from the coupler member in a state where both are attached to each other.
In this electrodeless discharge lamp, the base and the attachment member of the coupler member are respectively formed of synthetic resin, so that there is a risk that the electrodeless discharge lamp, if used for a long time, may decrease in strength due to degradation of the synthetic resin. Thus, it is considered that it becomes unable to securely fit the lamp part to the base and fit the coupler member to the base in the electrodeless discharge lamp.